This invention relates generally to quick-disconnect couplings and more particularly to a quick-disconnect coupling which is especially adapted for use in applications involving a combustible gas (e.g., natural or LP gas), the coupling having a heat-sensitive cutoff feature for shutting off gas flow when subjected to dangerously high temperatures.
Gas outdoor barbecue grills are typically fueled by natural or LP gas stored under pressure in portable refillable tanks or cylinders. Replacing an empty cylinder has heretofore been a relatively burden-some and time-consuming task, involving unscrewing and then screwing back together the various component parts of the connection (known in the trade as a "POL" fitting) between the cylinder and the gas line to the grill. Moreover, improper reconnection may result in dangerous gas leakage from the cylinder.
The use of a quick-disconnect coupling between the tank and the gas line to the appliance has been suggested as a solution to the above-mentioned problem. One particular coupling which has been proposed for such use includes a socket fitting for connection to the cylinder and a plug fitting for connection to the gas line. The socket has a passage therethrough, a valve seat in the passage and a one-piece poppet valve spring-biased to a closed position against the valve seat for blocking gas flow from the cylinder. The plug fitting comprises an elongate plug body which is receivable in the outlet end of the socket passage for engagement with the poppet valve to force it open, and a flange soldered to the plug body. Detent balls in the walls of the socket fitting are engageable with this flange for holding the plug and socket fittings in assembly. In the event the temperature of the coupling rises to a dangerously high level, the solder bond between the plug body and flange melts, enabling the spring-biased poppet valve to close by pushing the plug body downstream relative to the flange, which is retained in fixed position relative to the socket fitting by the detent balls.
While this automatic safety cutoff feature is desirable, the particular design described above is disadvantageous in that the plug body and gas line to which it is attached present a substantial amount of resistance to movement of the spring-biased poppet valve to its closed position. If the resistance is too great for the poppet valve spring to overcome, the cutoff mechanism will fail to operate.